/Engine/Plugins/Runtime/MeshModelingToolset/Source/ModelingComponents/Public/PreviewMesh.h
the current preview FDynamicMesh, and replace with a new empty mesh
[TUniquePtr](API\Runtime\Core\Templates\TUniquePtr)< [FDynamicMesh3](API\Runtime\GeometryCore\DynamicMesh\FDynamicMesh3) > ExtractPreviewMesh() const